Making Alum Crystals

EXPERIMENT SHEET, HOW TO MAKE ALUM GLASS

STEP BY STEP, ALUM CRYSTALS

Let's see how to make rock alum crystals. With these quantities you will be able to make many depending on which glasses you are going to add the solution in, or if you use a bigger one you will be able to make a single crystal but of a bigger size. To make it, you can watch the full video here, or read the step-by-step below:

                                                            MATERIALS

The only indispensable material that you may not have at home is the Rock Alum. The rest you can substitute with elements available at home.

• Rock Alum. You can see it in Alquera.com
• Glass or polypropylene beaker. You can use kitchen or laboratory beakers. See
• Sewing thread
• Colouring: You can use any type of colouring, either children's tempera or food colouring and it is optional only to colour the crystals.

STEP 1. PREPARE MIXTURE AND HEAT

• Prepare a mixture of 250gr of alum in 250ml of water in a saucepan where you are going to heat it. You can use other quantities, but always remember to add the same amount of water and the same amount of alum.
• Heat the water without boiling it (to avoid evaporation).
• Stir the mixture so that the alum is completely dissolved.

STEP 2. PUT THE MIXTURE IN A GLASS

• Once the alum is well dissolved, transfer it to a glass.
• You can add any colouring you like to the mixture and stir well. We have used a fluorescent dye (Rhodamine-b), but you can use any food colouring (children's, food,...).

STEP 3, PREPARE CRYSTALLISATION

• We now take a thread and place it inside the glass, holding it on the outside of the glass with a rod/pencil. On the thread is the element on which crystallisation will occur.
• Leave the glass with the thread to rest for 30 minutes. As it cools, we can see the result.

RESULT. ALUM CRYSTAL

After waiting for 30 minutes, we can see our alum crystal, it has a violet colour, due to rhodamine b, which fluoresces when it is illuminated with ultraviolet light. Here you can see it:

TECHNICAL EXPLANATION

Crystallisation is the process by which crystals are created from a powdered element. The basis of crystallisation is the greater solubility of an element at a higher temperature than at a lower temperature. Therefore, at a higher temperature, a greater amount of solvent can be dissolved.

As it cools down, the slower the better, the solubility of the alum decreases and a crystal will form around the thread. Wait at least 1/2h to see the results.

Since the crystal is formed by precipitation in a supersaturated solution, in order for the crystal to continue to grow, the crystal simply needs to be placed in another hot, supersaturated solution. As it cools, the crystal will continue to grow.